Belt fissure detection device

ABSTRACT

A conveyor belt fissure detection apparatus having a plurality of pairs of fissure detecting coils buried in a conveyor belt in the transverse or belt-width direction and buried in the belt in the longitudinal direction with the pairs of coils being positioned at uniform intervals along the length of the conveyor belt to detect a fissure when it occurs either in the transverse or longitudinal direction of the belt thereby breaking any of the detecting coils. An exciting coil, excited by an oscillator and receiving coils connected to a detector circuit are positioned in proximity of the conveyor belt in aligned relation with the belt detecting coils embedded in the conveyor belt to electromagnetically couple with them when they travel by in proximity to the exciting and receiving coils. A fissure in the conveyor belt is detected by a detector circuit when one of the coils in the belt is broken causing signal interruption indicative of an occurrence of fissure in the belt.

United States Patent 3,636,436

Kurauchi et a]. 45 1 Ja 18, 1972 [54] BELT FISSURE DETECTION DEVICE1,233,324 1/1967 Germany 310/259 [72] Inventors: Norm Kmuchi; Told who),both 1,146,108 3/1969 Great Britain ..l98/232 g: PrimaryExaminer-Rud0lph V. Rolinec s- Kouno Kasu ai a Qua Assistant Examiner-R.J. Corcoran g pan Attomey-Carothers and Cal-others [731 Assignees:Sumitomo Electric Industries, Ltd., Osaka;

Tokai Rubber Industries, Ltd., Komaki, [57] ABSTRACT Japan e A conveyorbelt fissure detection apparatus having a plurality [22] Filed: Mar. 31,1970 of pairs of fissure detecting coils buried in a conveyor belt inthe transverse or belt-width direction and buried in the belt in [21124,242 the longitudinal direction with the pairs of coils beingpositioned at uniform intervals along the length of the conveyor 52 us.Cl .;.....324/34, 198/232, 340/259 bell to detect a fissure when itOccurs either in the transverse [5i Int. Cl ..G0lr 33/00 0' longitudinaldireclion of the thereby breaking y of [53] Field f Search 324 3 11; 3 22 93 the detecting coils. An exciting coil, excited by an oscillator 3 0259 and receiving coils connected to a detector circuit are positionedin proximity of the conveyor belt in aligned relation 5 References citedwith the belt detecting coils embedded in the conveyor belt toelectromagnetically couple with them when they travel by in FOREIGNPATENTS OR APPLICATIONS proximity to the exciting and receiving coils. Afissure in the conveyor belt is detected by a detector circuit when oneof the coils in the'belt is broken causing signal interruptionindicative ofan Occurrence offissurein the belt 17 Claims, 23 DrawingFigures Pmmmmamz 31636436 SHEET BF 4 VEN Toes.

NOE! ram Kama 0cm, Tax/o Foam 70, KEN/cu! Yoshi/p4 MAsAM/rsu U1, ZENJINAGA TA 4' H mom zuAm/o (Aka M5254 0420 was THE/E A TTORNE vs BELTFISSURE DETECTION DEVICE BACKGROUND OF THE INVENTION 1 Field of theInvention The present invention relates to a device for electricallydetecting a fissure which may appear in an endless belt or the like usedin belt conveyance.

2. Description of the Prior Art It is well known that a conveyor beltfor conveyance of lumpy materials such as coal and other mineral ore issometimes torn by the impact of these lumpy materials loaded I the belt.In this instance, so long as no adequate measure is taken to detect afissured portion of the belt and the belt is continuously operated inthis condition, the fissure will develop over the entire length of thebeltwith the result that the belt will no longer be suitable for anytype of use.

In a belt conveyor having a travel belt span of more than 100 meters, itis practically impossible to station attendant workers along the beltfor the purpose of making a visual inspection of the belt in order totake precautions against a fissure occurrence on thesurface thereof.

Inorder to detect the occurrence of such belt fissures, belt fissuredetection devices have been conceived and two such examples are found inGerman Pat. No. 1,233,324 and US. Pat. No. 2,649,955.

According to the disclosure of the German patent, the belt fissuredetection apparatus comprises three loop detector coils buried in aconveyor belt all at right angles relative to the longitudinal length ofthe belt, two of these loop detector coils being over lapped by theremaining or third loop coil at two different positions. Permanentmagnets are positioned beneath the conveyor belt in correspondence withthese two positions, and three receiver coils are suitably disposed,such as beneath the conveyor belt, so as to be magnetically coupled witheach of the three respective loop coils.

Since the loop coils are excited by the permanent magnets,

the induced current often varies with change of the traveling speed ofthe belt accompanying an undesirable fading of the wave form of thiscurrent. In the case where an oscillating coil to be operated by thealternating current is employed, instead of the permanent magnets, theleakage flux of both loop coils couples to the receiver coils since theinterval between each SUMMARY OF THE INVENTION The present invention isdirected to eliminate the abovementioned defects inherent inconventional belt fissure detection apparatus and has for the principleobject to provide an improved belt fissure detection apparatuscomprising an excitor coil and two receiver coils positioned adjacent tothe bottom surface of the belt, a pair of loop coils embedded in theconveyor belt to be electromagnetically connected with said excitor andreceiver coils, one coil being buried in the belt in the longitudinaldirection of the conveyor belt adjacent to one edge of the belt whilethe other coil is buried in the belt at right angles relative to thefirst-mentioned loop coil and overlapped at its one end by thecorresponding end of the firstrnentioned loop coil. The arrangement issuch that, when the overlapped ends of the loop coils travel just overthe excitor coil as the belt is being driven, the other end of each ofthe loop coils also travels just over the respective receiver coils sothat when an electromagnetic coupling between at least one of said loopcoils and the corresponding receiver coil is broken, a fissureoccurrence in the belt can be readily detected.

Another object of the present invention is the provision of beltfollower means incorporated in the belt fissure detection device forestablishing the above-mentioned arrangement of loop coils to be inregister with the excitor and receiver coils to compensate for beltmeandering even where the conveyor belt is employed to travel along acurved path.

Still another object of the present invention is to provide a Isufficiently durable wiring material for the loop coils to be buriedwithin the belt, which may be employed in connection with the fissuredetection device comprising this invention.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages appearhereinafter in the following description and claims. 7

The accompanying drawings show, for the purpose of exemplificationwithout limiting the invention or the claims thereto, certain practicalembodiments illustrating the principles of this invention wherein:

FIG. I is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cut away showing the employment of the loop detectioncoils and their relationship with the excitor and receiver coils, beingthe principle embodimenof the present invention;

FIG. 2 is a full cross-sectional view of the conveyor belt of FIG. 1taken along the line 2-2 of FIG. 1;

FIG. 3 are schematic diagrams of wave forms (m) and (n) of theelectricsignals respectively sensed by the receiver coils of the belt fissuredetection apparatus comprising this invention;

FIG. 4 is a block diagram of the circuit comprising the belt fissuredetector unit; I

FIG. 5 is a perspective view representative of an excitor coil or one ofthe receiver coils employed in the belt fissure detection apparatuscomprising this invention;

FIG. 6 is a circuit diagram of the excitor coil or one of the receivercoils shown in FIG. 5;

FIG. 7 is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cutaway depicting a modified embodiment of the presentinvention;

FIG. 8 is a full cross-sectional view of the conveyor belt of FIG. 7taken along the line 8-8 of FIG. 7; I

FIG. 9 is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cutaway depicting a still further modified embodimentof the present invention;

FIG. 10 is a full cross-sectional view of the conveyor belt of FIG. 9taken along the line 10-10 of FIG. 9;

FIG. 11 is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cutaway and depicting belt follower means;

FIG. 12 is a full cross-sectional view of the conveyor belt of FIG. 11taken along the line 12-12 of FIG. 11;

FIG. 13 is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cutaway depicting a further modified embodiment of thepresent invention;

FIG. 14 is a full cross-sectional view of the conveyor belt of FIG. 13taken along line 14-14 of FIG. 13;

FIG. 15 is a plan view of a portion of a conveyor belt with a sectionallayer of the belt cutaway depicting a still further modified embodimentof the present invention;

FIG. 16 is a full cross-sectional view of the conveyor belt of FIG. 15taken along the line l6-l6 of FIG. 15;

FIG. 17 is a longitudinal sectional side view of the conveyor belt ofFIG. 15 taken along the line I7l7 of FIG. 15;

FIG. 18 shows a portion of a wire material for the coils buried in thebelt in accordance with the present invention;

FIG. 19 is a cross-sectional view of an end portion of the wire materialshown in FIG. 18 taken along the line 1919 of FIG. 18;

FIG. 20 shows a portion of a modified wire material for the coils inaccordance with the present invention;

FIG. 21 shows a portion of another modified wire material for the coilsin accordance with the present invention;

FIG. 22 shows a portion of still another modified wire material for thecoils in accordance with the present invention; and

FIG. 23 in a cross-sectional view of the wire material of FIG. 22 takenalong the line 2323 of FIG. 22

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is made to FIGS. 1and 2 showing the belt fissure sensing apparatus wherein there is showna conveyor belt I with a loop coil 2 buried within the conveyor belt 1in the longitudinal direction of the belt adjacent and along one edge ofbelt 1 and including sensor portions 3 and 4, which are served by bothends of the loop coil 2. A pair of wires 5 connect in series the sensorportions 3 and 4. A loop coil 6 buried in the same conveyor belt 1 ispositioned at a right angle relative to the loop coil 2 along the widthof the conveyor belt and includes sensor portions 7 and 8, which areserved by both ends of the loop coil 6. The sensor portion 7 isoverlapped by the sensor portion 3 of the loop coil 2. A pair of wires 9connect in series the sensor portions 7 and 8.

A plurality of such coil units consisting of the loop coils 2 and 6 ashereinbefore described are buried in the belt 1 in the longitudinaldirection over the entire length thereof at suitable intervals, forexample, in the range of every 20 to I00 meters. Obviously this range ofintervals can be of greater or lesser magnitude.

An excitor coil indicated at A is connected with an excitor means. Thereceiver coils indicated at B & C are respectively connected toterminals B, & C receiver units 41 and 42 as shown in FIG. 4. Thisarrangement is such that, when the overlapped sensor portions 3 and 7travel over the excitor coil A as the conveyor belt 1 is being driven,the other sensor portions 4 and .8 also simultaneously travel over thecorresponding receiver coils B and C.

In this arrangement, when a sinusoidal oscillating current ofapproximately 10 kHz. to 100 kHz. or more is applied to each excitorcoil A from the excitor means, this current will be transmitted to eachof the receiver coils B and C by magnetic induction.

Signals having the wave forms m and n" shown in FIG. 3, will be produceddue to the movement of the conveyor belt I, which signals are receivedby the receiver coils B and C and are transmitted, respectively, to twoinput terminals marked B. and C." of the detecting circuit of FIG. 4.

When at least one fissure appears in the conveyor belt 1 and any one ofthe wires 5 and 9 of the pairs of loop coils is thereby broken, nocurrent is transmitted to the corresponding receiver coil B or C. Thus,the fissure is then detected by the detection circuit.

FIG. 4 shows a circuit diagram of the belt fissure detector unitcomprising this invention and includes a logic circuit for detecting afissure occurrence in the belt which operates an annunciator device andfinally automatically stopping the conveyor belt drive means. I

As described previously, when the sensor portions 3 and 7, and alsosensor portions 4 and 8 of the loop coils 2 and 6 come in proximalposition to be electromagnetically coupled with the excitor coil A, andthe receiver coils B and C, respectively, the magnetic induction takesplace so as to transmit the current from the excitor coil to thereceiver coils through the respective pairs of wires 5 and 9. On theother hand, when a fissure occurs in the belt and any one of the wires 5and 9 is consequently broken, no induced current is transmitted throughthe loop coil of that wire which is broken and the respective receivingcoil does not receive a signal m" or n.

However, assuming that no fissure occurs in the belt and accordingly nobreakage of the wires of the loop coils takes place, the receiver coilsB and C produced an induced signal by the oscillating current passingthe excitor coil A through the respective loop coils 2 and 6 so as togenerate pulse signals having respective wave forms, as shown in FIG. 3,through the respective receiver units 41 and 42 wherein the signalsdetected by the receiver coils are first amplified and then sent througha shaper circuit as indicated in FIG. 4. Then, the shaped amplifiedpulse signals are in turn directed to an OR" circuit and an AND circuit,respectively, in the logic circuit unit 52. So long as this no-fissurecondition continues, the OR- and AND-gate circuits 43 and 44,respectively, continue to produce output signals, the output signal fromthe OR-circuit 43 being fed to a differentiation circuit 45 which actsto transform the received signal into a sharp positive pulse which is inturn fed to a ,set terminal S of a bistable flip-flop circuit 48. Theoutput signal from the AND-circuit 44 is fed to a delay circuit D andthen to a differentiation circuit 47 which acts to transform thereceived signal into a sharp positive pulse which is in turn fed to thereset terminal R of the bistable flip-flop circuit 48 in a constantlydelayed condition.

On the contrary, when any one of the wires 5 and 9 of the loop coils 2and 6 is broken, the AND-circuit 44 will not generate therefrom anyoutput signal sincethere is no simultaneous coincident of signals fromthe receiver units 43 and 44 on the two inputs to the AND-gate circuit44, and, therefore, no input current is supplied to reset terminal R ofthe flip-flop circuit 48. As a result flip-flop circuit 48 will generatean output signal of constant value. The output signal of constant valuefrom the flip-flop circuit 48 is then fed to an integrator circuit 49.

The integrator circuit 49 acts to integrate the constant value of theoutput signal from the flip-flop circuit 48 for a specified time, whichwill be in turn compared with the standard value of the current in acomparison circuit or comparator 50. When the integrated value of theoutput signal from the flipflop circuit exceeds the standard value setat the comparator, a relay 51 will be operated to actuate an annunciatorsuch as the buzzer 54 raising an alarm while a holding circuit 53,included in the annunciatorconsole 55 together with the buzzer 54, ismaintained in its operative condition to maintain the buzzer 54 inoperation. At the same time, if desirable, the output signal from therelay 51 will operate another relay 56 to open-switch 57 to cease theoperation of motor 58 driving the conveyor belt.

So long as none of the wires of the loop coils 2 and 6 is broken, thereceiver coils B and C normally receive their respective signals at thesame time, which signals are fed simultaneously to the OR-circuit 43and'the AND-circuit 44 included in the logic circuit unit 52.

As previously described, with signal reception through the receiver coilB, the OR-circuit43 will always generate an out put signal to thedifferentiation circuit 45 wherein the output signal of which isdifferentiated so as to produce a sharp-positive pulse which is suppliedto the set terminal S of the bistable flip-flop circuit 48. On the otherhand, with signal reception through the receiver coil C as well as fromthe receiver coil B, the AND-circuit 44 will generate an output signalto the delay circuit D wherein a retardation time of small value is.imparted to the output signal. This delayed signal will be then suppliedto the differentiation circuit 47 wherein this signal is differentiatedso as to produce a sharppositive pulse which is in turn supplied to thereset terminal R of the bistable flip-flop circuit 48, causing theflip-flop circuit to be placed in its reset condition.

While the pulse signal is supplied from the differentiation circuit 45to the set terminal S of the flip-flop circuit 48 and the pulse signalfrom the differentiation circuit 47 to the reset terminal R of the same,the flip-flop circuit is maintained in its inoperative or "low"condition and therefore inoperative on integrator circuit 49.

FIGS. 5 and 6 show details of construction of the excitor coil, whichconstruction is also identical to that of either of the receiver coils Band C as above disclosed. FIG. 5 is a perspective view of the coil andFIG. 6 is a circuit diagram representative of the coil.

The excitor coil and receiver coil have the identical construction inthe present invention.

FIG. 5 is a perspective view of the structure of the coil assemblyhaving primary coil 12 and secondary coil 11 of the excitor coil orreceiver coil, whatever the case may be.

In FIG. 5, the ferrite core 10 may, have the dimensions of 2,500 squaremillimeters and 50 millimeters in length. The secondary coil L ofenameled wire 11, 0.1 mm. in diameter, is wound around the ferrite core10 approximately 70 turns, and the primary coil L, of enameled wire 12of the same diameter wound around die ferrite core 16 approximately twoturns to couple magnetically with the secondary coil L The primary coilL is connected to an oscillating source or the detector circuitdepending upon whether the structure is to be employed as an excitorcoil or a receiver coil.

In FIG. 6, the secondary coil L provides a resonance circuit togetherwith the capacitors C,, C C and C and is magnetically coupled with theprimary coil L,, the latter being connected to an oscillating source inthe case of an excitor coil, or connected to a detector circuit in thecase of a receiving coil.

' For example, when the circuit shown in FIG. 6 uses the coils as shownin the FIG. 5 and capacitors C,, C have a value of 800 pf.,respectively, and variable capacitors C C, have a variable value of80-3,000 pf., respectively, a resonance circuit having a tuningfrequency of 200 kHz. is provided.

In the case where the coil assembly shown in FIG. 5 is employed as anexcitor coil, the primary coil L, of the coil assembly is connected toan oscillating source and a large resonance current flows in thesecondary coil L which is magnetically coupled with the primary coil L,.The core of the coil assembly provides magnetic flux due the resonancecur rent of the secondary coil L Since the coil assembly of the excitorcoil is placed in proximity to the moving conveyor belt in which thebelt fissure detecting coils are embedded, the magnetic flux of the coilassembly of the excitor coil is magnetically interlinked with the beltfissure loop coils 2 and 6 to induce a current in the receiving coils Band C.

On the other hand, in the case where the coil assembly shown in FIG. 5is used as a receiver coil B or C, the secondary coil L is coupled withthe magnetic flux which accompanies the induced current in the fissureloop coils 2 and 6 embedded in a moving conveyor belt placed inproximity to the coil assembly and a resonance current is induced in thetuning circuit by the secondary coil L The resonance current of thesecondary coil L induces a current in the primary coil L, to be suppliedto the detector circuit.

It has been largely understood that a fissure, if any, often appears onthe belt surface in the longitudinal direction thereof rather than inthe cross or lateral direction. Accordingly, one of the loop coils suchas 2 which is buried in the belt along one edge of the conveyor belt 1in accordance with the present invention is seldom susceptible tobreakage while the other of the loop coils such as 6 which extends inthe cross lateral direction thereof is more susceptible to breakage.Thus, so long as a pair of the loop coils 2 and 6 are buried in the beltin the L-shaped relationship in accordance with the present in vention,the number of necessary loop coils to be employed along the length ofthe conveyor belt can be reduced resulting in the reduction of the totalnumber of necessary excitor coils and receiver coils disposed oremployed over the entire length of the conveyor belt.

In addition, since a sufiicient space interval is provided between theexcitor coil A and the receiver coil C over the entire width of the beltand since a sufficient interval is provided between the excitor coil andthe receiver coil B in the longitudinal direction of the belt, these twodifferent intervals being substantially equal to the distancetherebetween, interference of electromagnetic connection between theexcitor coil and either of the receiver coils can be substantiallyprevented so that sensitive detection of a fissure appearing in the beltcan be ensured.

However, according to the embodiment as disclosed in FIG. I, the onlycondition when a fissure occurring in the conveyor belt cannot bereadily detected is where the break occurs at the overlapping sensorportions 3 and 7 of the loop coils 2 and In order to provide fordetection at this point of overlapping sensor portions 3 and 7, thearrangement of the loop coils 2 and 6 may be modified like that shown inFIG. 7 and FIG. 8, wherein elements comprising the belt fissure sensingdevices are identical to that previously disclosed in FIG. I, beingdesignated by the same numerals and symbols.

Referring now to FIG. 7 and FIG. 8, a plurality of the loop coils 2 and6 in L-shaped pairs are buried'in the conveyor belt l at a suitableintervals along the length of the conveyor belt,

for example, in the range of 20 to 100 meters, one of the loop coils 2being adjacent to and along one edge of the conveyor belt while theother loop coil 6 being positioned across the width of the conveyorbelt. However, in this instance, the sensor portion 7 of the loop coil 6and the sensor portion 3 of the loop coil 2 are placed in spacedrelationship, for example, a spacing distance indicated at e," being avalue of approximately 5 to 10 millimeter measured in the direction ofthe width of the conveyor belt. Despite the spacing "e" existing betweenthe sensor portions 3 and 7, the excitor coil A is arranged beneath theconveyor belt 1 so as to be in register with an end portion of each ofthe sensor portions 3 and 7 in the conveyor belt as the belt is drivenover the excitor coil A.

As to the arrangement of the other parts and operation of the fissuredetection circuit, this is the same as disclosed in connection with FIG.1 through FIG. 4.

Although in this instance only the excitor coil A is employed withrespect to the loop coils 2 and 6, a pair of separate excitor coils maybe employed with a single excitor means for each sensor portion 3 and 7.

With the spacing e" provided as such, the sensor portions 3 and 7 cannotpossibly be broken at the same time. Therefore, effective detection ofthe fissure occurrence in the belt can be ensured as against the casewhere the sensor portions 3 and 7 are in an overlapped relation to eachother shown in FIG. 1.

However, there is another disadvantage made present in connection withthe-FIG. 7 embodiment, in that, when a fissure appears in the belt inthe longitudinal direction running through the spacing e, neither of thesensor portions are broken and, accordingly, the fissure detectioncircuit is incapable of operating the annunciator unit and indicatingthe occurrence of a fissure through spacing e. Therefore, accuratedetection of a fissure occurring in this instance is not possible. Inorder to eliminate this particular disadvantage, the arrangement of theloop coils 2 and 6 may be further modified as shown in FIGS. 9 and 10,wherein, again, elements comprising the belt fissure sensing apparatusare identical to those previouslydescribed with like elements beingdesignated by the same numerals and symbols.

As shown in FIGS. 9 and 10, the component parts comprising the pairs ofloop coils 2 and 6 buried in the conveyor belt are the same as those 2and 6 mentioned in connection with the embodiment shown in FIG. 1, butthe loop coils of one pair, generally designated as Y, and the adjacentpair, generally designated as Z, are disposed in an oppositely opposedbut adjacent relationship separated by a distance T. One of the loopcoils 6 and 6 of each respective pair of loop coils Y and Z is disposedin the conveyor belt in a transverse direction as compared to the coils6 in the first-mentioned em bodiment shown in FIG. 1 wherein the loopcoil 6 is disposed normally relative to the longitudinal direction ofthe conveyor belt.

In other words, as can be understood from FIG. 9, the loop coil 2 of onepair of loop coils Y and the loop coil 2' of the adjacent pair of loopcoils Z are respectively positioned along opposite edges of the conveyorbelt in the longitudinal direction. However, the loop coils 6 and 6 ofthe adjacent pairs Y and Z, respectively, have respective angles 6,, Brelative to the normal construction lines X, separated by the distanceindicated as T and passing through the center of the overlapping sensorportions 3 and 7, or 3' and 7' at right angles to the longitudinaldirection of the conveyor belt.

The general arrangement of the loop coils 2 and 6, and 2 and 6 of eachrespective pair Y and Z relative to the corresponding excitor coils A orD and the corresponding receiver coils B and C or E and F is the same asdescribed previously in connection with the first-mentioned embodimentshown in FIG. I. v v

In this instance, the excitor coils A and D are connected to a commonoscillating current source, the receiver coils B and E are connected toa common input terminal, such as B, of the receiver unit 41 shown inFIG. 4 while the receiver coils C and Fare connected to a common inputterminal, such as C, of the receiver unit 42 shown in the same figure.

According to the embodiment shown in FIG. 9, since each of the loopcoils.6 and 6' is angularly disposed relative to the construction linesX, no interferencebeeause of magnetic flux occurs between these coilseven when the conveyor belt 1 is in operation. 7 I

In addition, even if a fissure occurs in the conveyor belt at a positioncorresponding to the overlapping sensor portions 3 and 7 or 3' and 7 toan extent that the both loop coils 2 and 6 or, 2' and 6 of one of therespective pairs of loop coils Y orZ are entirely broken, the detectionof the fissure occurrence can be ensured by the loop coils of the nextor adjacent pair.

' The loop coil arrangements as above disclosed in connection with theembodiments of FIGS. 1, 2, and 7 through FIG. 10 are incapable ofreliably ensuring fissure detection upon occurrence of such a fissureand subsequent breakage of one of the loop coils, where the conveyorbelt is laterally meandering while it travels along its conveyor path.This is because, when the conveyor belt is laterally meandering duringits travel, any one of the sensor portions 3 and 7, or 4 or 8, which areserved by the both ends of each loop coil 2 and 6 and initiallypositioned in register with the excitor and receiver coils A, B & C ashereinbefore described, is laterally displaced from a position in therange of effective electromagnetic coupling with excitor and receivercoils A, B & C.

However, the arrangement as shown in FIG. 11 and FIG. 12 facilitatesfissure detection even where the conveyor belt is laterally meanderingduring its course of travel in such a manner that the excitor andreceiver coils are caused to follow the meandering travel of theconveyor belt in constant aligned register with the loop coils buried inthe conveyor belt by employment of conveyor belt follower means engagingthe longitudinal edges of the belt.

As shown in FIGS. 11' and 12, the follower means comprises a pair ofcarriages .1-3 and 13', each have two pairs of wheels 16 to support thecarriages for movement along the rails 17 in a direction normalto thelongitudinal direction of the conveyor belt. The carriages 13 and 13'are connected to each other for their travel on the rails 17 by means ofa connecting rod 18. The ends of rod 18 are pivotally connected to eachcarriage. A pair of guide rollers 14 and 14' rotatably supported fromthe carriage 13 and 13', respectively, by means of support members and15' are set to engage the longitudinal edges of the conveyor belt 1.

The excitor coil A and the receiver coils B and C are mounted on therespective carriages 13 and 13 in such a manner that the sensor portion8 of the loop coil 6 is in registerwith the receiver coil C mounted onthe carriage 13, while the overlapping sensor portions 3 and 7 of bothloop coils 2 and 6 and the sensor portion 4 of the loop coil 2 are,respectively, in register with the excitor coil A and the receiver coilB mounted on the carriage 13', regardless of whether or not the conveyorbelt 1 is meandering along its path of travel.

In practice, when the conveyor belt 1 is actually meandering in adirection normal to the longitudinal length of the belt during itsnormal travel operation, one edge of the conveyor belt I will bedirected against the guide roller of one of the carriages l3 and 13'causing the carriages, as connected, to move i n-the same lateraldirection as the belt is meandering, the distance of the lateralmovement of the carriages corresponding to the actual distance of thelateral movement of the conveyor belt I.

Thus, the excitor and receiver coils A, B and C mounted on therespective carriages l3 and 13 are caused to continuously follow therespective sensor portions 3, 4, 7 and 8 of the loop coils 2 and 6 so asto, at all times, electromagnetically couple the excitor coil A to thereceiver coils B and C with the embedded loop coils 2 and 6 throughoutthe meandering movement of the conveyor belt 1; thereby insuring fissuredetection in the conveyor belt.

FIGS. 13 and l4show an embodiment compensating for conveyor beltmeandering to insure fissure detection in the belt but eliminating thenecessity of providing the conveyor belt follower means of FIGS. 11 and12.

In the arrangement shown in FIGS. 13 and 14, each one of the loop coils19, 20 and-21 buried in the conveyor belt 1, is positioned therein toform a rectangle or square or quadrangular configuration so that loopcoil 19 has four sides, 22, 23, 24 and 25, loop coil 20 has four sides,26, 27, 28 and 29, and loop coil 21 has four sides, 30, 31, 32 and 33.

The quadrangular-shaped loop coil 19 has a pair of coil sides 22 and 23extending in a direction normal of the con veyor belt 1 in spacedparallel relation to each other and a pair of the coil sides 24 and 25extending in the longitudinal direction of the conveyor belt I, eachalong an edge of the conveyor belt and in parallel relationship. Thequadrangularshaped loop coils 20 and 21 are, in a similar manner,provided with a pair of thecoil sides 26 and 27 and 30 and 3],respectively, extending in the normal direction of the conveyor belt anda pair of the coils sides 28 and 29 and 32 and 33, respectively,extending in longitudinal direction of the conveyor belt.

The three loop coils 19, 20 and 21 are buried in the conveyor beltl insuch a manner that the side 22 of the loop coil 19 is suitably spacedfrom the parallel aligned sides 26 and 30 of the respective loop coils20 and 21 while the side 29 of the loop coil 20 and the side 32 of theloop coil 21 are suitably spaced from each other in parallel alignedfashion.

In practice, a plurality of these three loop coils 19, 20 and 21,representing one unit are buried in the conveyor belt 1 along the lengthof belt at spaced intervals, as previously mentioned in connection withprior embodiments comprising this invention.

In FIGS. 13 and 14, the reference symbols G and H indicate excitor coilsfor connection to a single oscillating current source. The receivercoils J, K and P are connected to the belt fissure detector circuit.

The arrangement of the excitor coils-and receiver coils with respect tothe quadrangular-shaped loop coils is suchthat the adjacent sides 22, 26and 22, 30 of the loop coils pass over the excitor coils G and H,respectively, during the travel of the conveyor belt, at the sameinstance when the sides 23, 27 and 31 of the loop coils pass over thereceiver coils J and K and P, respectively.

In this arrangement, assume that a fissure occurs along the positionindicated at I. When a sinusoidal oscillating current of approximately10 kHz. to I00 kl-lz. or more is applied to the excitor coils G and H, abreak occurs in the sides 22, 26, or 27 of the loop coils 19 and 20andthe induced current is only received by the receiver coil P. If thefissure appears at a'position indicated by II and a break appears in theside 22 of the loop coil 19, an induced current is received by thereceiver coil J. If thefissure appears at a position indicated by Illand a break appears in the sides 22, 30, or 31 of the loop coils 19 and21, an induced current is only received by the receiver coil K.Therefore, by handling the receiver current of the receiver coils J, Kand P, detection of the fissure appearing on the belt surface at anyposition over the entire width of the conveyor belt can be reliablyinsured, regardless whether or not the conveyor belt is laterallymeandering during its progressive conveyor travel. In addition, sincethe distance between each of the excitor coils and the correspondingreceiver coils may be adjusted by changing the length of each pair ofthe sides 24, 25; 28, 29; and 32, 33 of the respective loop coils 19, 20and 21 in the longitudinal direction of the conveyor belt 1,interference between the direct electromagnetic coupling,between theexcitor coil and any one of the receiver coils is prevented.

With reference to FIG. 15 through FIG. 17, the actual details ofconstruction of a typical belt fissure detecting unit is described. Theconveyor belt 1, in this instance being L200 mm. in width (W), l5 mm. intotal thickness (1) and l,060 m. in overall length, comprises a nylonfabric core 28 which includes five plies of cotton duck. The undersurface 29 of the conveyor belt 1 consists of a rubber layer 30positioned below of 900 mm.

the nylon fabric core 28. The conveyor belt has a rubber covering orlayer 35 positioned above the nylon fabric core 28, the thickness of therubber layer being approximately 3.2 mm.

The loop coil 2 is extended in the longitudinal direction along one edgeof the belt and is spaced 30 mm. (a) from the conveyor belt edge and hasthe length (L,) of 1,000 mm., a width ((1,) of 100 mm. and the magnitudeof reactance is 0.1 to 1.0 mh. The loop coil 6 extending in a directionnormal to the longitudinal direction of the conveyor belt 1 has its coilend 7 overlapped by the corresponding coil end 3 of the loop coil 2.Loop coil 6 has a length (1. of 1,140 mm., the width (d,) of 100 mm. andthe magnitude of reactance is 0.1 to 1.0 mh. Both ends of the loop coil6 are spaced 30 mm. (a,b) from the respective edges-of the conveyorbelt. Both loop coils 2 and 6, are of course, buried in the belt, andare horizontally positioned with the lower rubber covering or layer 30at a horizontal level of 3 mm. above the under surface 29 of theconveyor belt, the distance between the under surface to the coils beingindicated by (i) in FIG. 17. A plurality of these coil units 2 and 6 arearranged in the interior of the belt in the longitudinal direction atsuitable intervals (L of 20 m. for the entire length of the conveyorbelt.

An excitor coil A is connected with an oscillating device having theoutput capacity of I mw. for supplying a current having a frequency of100 kc. The receiver coils B and C are connected with a single beltfissure detection device having the detection capacity of 0 to 100 db.The excitor coil A is positioned at a suitable spaced interval(h)'within the range of 50 to 100 mm. below the under surface 29 of theconveyor belt. The receiver coils B and C are similarly disposed belowthe under surface 29 of the conveyor belt and spaced from each other atan interval (L of 1,040 mm. A distance (L,,) is maintained between theexcitor coil A and the receiver coil B Although the loop coils areburied in the belt at a position below the nylon fabric core 28, theymay also be buried at a position above the nylon fabric core 28, namely,in the upper rubber covering or layer 35. However, in the case wherematerial for the core 28 is employed is a steel cord, it is desirable toembed the loop coils 2 and 6 at a position below the steel core in thelower layer 30.

The details of the wiring material for the loop coils employed inconnection with the belt fissure detection apparatus in accordance withthe present invention is disclosed with reference to FIG. 18 throughFIG. 23.

It has been well known that a conveyor belt is frequently subjected,during its operation, to repeated positive and negative bending and alsoto impacts of loads carried by the belt as the conveyor belt is beingpassed over various pulleys, such as the drive pulleys, the headpulleys, the takeup pulleys, the bend pulleys and the snab pulleys.Furthermore, in the case where the belt is to be guided bytrough-forming idlers, the belt is subjected to a repeated bending inthe direction normal to longitudinal length of the conveyor belt.

In view of this, wiring material for the loop coils buried in theconveyor belt should be of sufficient durability. If any one of the loopcoils is easily broken by a cause other than a fissure appearing on thebelt surface, the belt fissure detector circuit will cause operation ofthe annunciator being representative of the occurrence of a fissure inthe belt, which is, in this case, not correct. Therefore, weak wiringmaterial for the coils 2 and 6 cannot be employed in order to achievethe objectives of the present invention.

Referring first to FIGS. 18 and 19, a core 31 having sufficientductility resistance against bending fatigue and made of a strand ofyarns of fiber such as polyester, nylon, or glass fiber is provided. Aconductive wire 32 with a covering 36 made of suitable material having ahigher electric conductivity, for example, a copper alloy in the form ofa fine wire or foil strip, is spirally wound around the core 31.

As previously described, since the fine wire is spirally wound around aresilient core material having sufficient ductility and resistanceagainst bending fatigue, the durability and shock resistance of theconductive wire 32 in combination with the ore3l is materially improved.

Another form of the wiring material is shown in FIG. 20 which is aconductive wire consisting of a copper alloy and spirally wound in aform as depicted in FIG. 20.

The spirally wound wiring material thus formed has imparted theretogreater flexibility and extensibility and, therefore, possessesexcellent shock resistance and durability when subjected to conveyorbelt flexion and bending.

Another form of the wiring material is shown in FIG. 21 which comprisesthe twisting together of two copper alloy wires in the manner shown.

Since two wires are twisted together, unidirectional flexibility isimparted to the wire combination together with increased extensibility,and therefore, the two-wire combination has excellent shock resistanceand durability when subjected to normal conveyor belt flexion andbending.

FIGS. 22 and 23 show a still further form of wiring material foremployment in the construction of the loop coils 2 and 6 wherein thereis provided shoot yarns 33 for supporting a plurality of the wiringmaterials of FIG. 18 in the form of a single flat band as indicated inFIG. 23.

Even if some of wires 37 are broken by external causes such as localwearing or scratching, the rest of the wires 37 will compensate for sucha breakage to insure proper belt fissure detection. 1

We claim:

l. A belt'fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire'length of said belt, said first loopcoil extended in the longitudinal direction of said conveyor belt andadjacent to and along one edge of said conveyor belt and said secondloop coil extended in a direction at right angles relative to said firstloop coil, one end of said second loop coil being overlapped by acorresponding end of said first loop coil adjacent to said conveyor beltedge, and excitor coil connected to an oscillating current source andpositioned in proximity to said overlapped loop coil ends of said firstand second loop coils, a pair of receiver coils connected to respectiveterminals of a belt fissure detector circuit and positioned in proximityto the other ends of said first and second loop coils, the arrangementof all of said coils being such that, when said overlapped loop coilends travel in proximity near said excitor coil as said conveyor belt isbeing driven, said other loop coil ends at the same time travel inproximity with respective of said receiver coils to provide anelectromagnetic coupling circuit between said excitor coil and saidreceiver coils through said loop coils to produce a pair of electricalsignals whereby the occurrence of a fissure in said conveyor belt can bedetected by said detector circuit.

2. The belt fissure detection apparatus of claim I wherein said electricsignals received by said receiver coils are respectively applied to anOR circuit and an AND circuit, in said detector circuit the outputsignal of said OR circuit being applied to a set terminal of a bistableflip-flop circuit while the output signal of said AND circuit applied toa reset terminal of said bistable flip-flop circuit through a delaycircuit, the output signal of said flip-flop circuit beingrepresentative of a breakage of any one of said loop coils embedded insaid conveyor belt.

3. The belt fissure detection apparatus of claim I, wherein each of saidloop coils embedded in said conveyor belt comprises a wiring elementconsisting of a resilient fiber core and a fine conductive wire in theform of strip or foil spirally wound around said core.

4. The belt fissure detection apparatus of claim 1, wherein each of saidloop coils embedded in said conveyor belt comprises a wiring elementconsisting of two lengths of twisted fine conductive wire in the form ofstrip or foil spirally wound around a resilient fiber core.

5. The belt fissure detection apparatus of claim 1, wherein each of theloop coils comprises a wiring element consisting of ill a resilientfiber core and a plurality of fine conductive wires in the form of afoil spirally wound around said core, said plurality of wires beingarranged in parallelalignment and bound together by shoot yarns toprovide a band.

6. The belt fissure detection apparatus of claim 1, wherein each of saidreceiver coils or said excitor coil comprises a primary winding formedaround a ferrite core and a secondary winding formed around said ferritecore adjacent said primary winding, said secondary coil winding forminga resonance circuit, in resonance with the excitor frequency imposedupon said primary coil.

7. A belt fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire length of said belt, said first loopcoil extended in the longitudinal direction of said conveyor belt andadjacent to and along one edge of said conveyor belt and said secondloop coil extended in a direction at right angles relative to said firstloop coil, one end of said second loop coil being adjacently spaced froma corresponding end of said first loop coil an excitor coil con-- nectedto an oscillating current source and positioned in proximity to both ofsaid spaced loop coil ends of said first and second loop coils, a pairof receiver coils connected to respective terminals of a belt fissuredetector circuit and positioned in proximity to the other ends of saidfirst and second loop coils, the arrangement of all of said coils beingsuch that, when said spaced loop coil ends travel in proximity near saidexcitor coil as said conveyor belt is being driven, said other loop coilends at the same time travel in proximity with respective of saidreceiver coils to provide an electromagnetic coupling circuit betweensaid excitor coil and said receiver coils through said loop coils,whereby the occurrence of a fissure in said conveyor belt can bedetected by said detector circuit.

8. A belt fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire length of said belt, said first loopcoil first extended in the longitudinal direction of said conveyor beltand adjacent to and along one edge of said conveyor belt and said secondloop coil extended in a direction at right angles relative to said firstloop coil, one end of said second loop coil being adjacently spaced froma corresponding end of said first loop coil, an excitor coil capable ofgenerating two electrical signals of different frequencies andpositioned in proximity to said adjacently spaced first and second loopcoil ends, a pair of receiver coils connected to respective terminals ofa fissure detector circuit and positioned in proximity to the other endsof said first and second loop coils, the arrangement of all said coilsbeing such that, when said adjacently spaced loop coil ends travel inproximity to said excitor coil as said conveyor belt is driven, saidother loop coil ends at the same time travel in proximity withrespective of said receiver coils to provide an electromagnetic couplingcircuit between said excitor coil and said receiver coils through saidloop coils, whereby signals received by said receiver coils are appliedto circuit filter means for discriminating between said signals due todifferent frequencies and thereafter applied to respective terminals ofsaid detector circuit 9. A belt fissure detection apparatus comprising apair of loop coils embedded in a conveyor belt, one of said coilsextended in the longitudinal direction of said belt and adjacent to andalong one edge of said belt, the other of said coils extended in adircction transverse to the longitudinal direction of said belt andhaving one end in overlapped relationship with one end of thefirst-mentioned loop coil, a second pair of loop coils embedded in saidbelt at a position adjacent to the firstmentioned pair of loop coils,one of said coils of said second loop coil pair extended in thelongitudinal direction of said belt, the other of said coils of saidsecond loop coil pair extended in a direction transverse to thelongitudinal direction of said belt and having one end in overlappedrelationship with one end of the first-mentioned loop coil of saidsecond loop coil pair, excitor coils each capable of generating anelectric signal of oscillating current and each respectively positionedin proximity to one of said overlapped ends of said first and secondloop coil pairs, two pairs of receiver coils, each pair connected torespective terminals of a fissure detector circuit and each respectivelypositioned in proximity to the other ends of said loop coils of each ofsaid loop coil pairs, the arrangement of all of said coils being suchthat, when said overlapped loop coil ends of each of said loop coilpairs travel in proximity near their respective excitor coil as saidconveyor belt is driven, said other ends of said loop coils of each ofsaid loop coil pairs at the same time travel in proximity to theirrespective receiver coils to provide an electromagnetic coupling circuitbetween each of said excitor coils and each of said receiver coilswhereby the occurrence of a fissure in said conveyor belt can bedetected by said detector circuit.

10 A belt fissure detection apparatus comprising a plurality of loopcoil members each of quadrangular configuration and together comprisingone unit embedded in a conveyor belt and disposed at suitable intervalsover the entire length of said belt, the first member of said loop coilsincluding a pair of coil sides extending in the longitudinal directionof said belt in spaced parallel relation to each other and a second pairof the coil sides extending in a direction transverse of thelongitudinal direction of said belt, the second member of said loopcoils including a pair of coil sides extending in the longitudinaldirection of said belt in spaced parallel relation to each other,

one of said coil sides in spaced parallel and adjacent relation to oneof the longitudinal coil sides of said first member, and a second pairof coil sides extending in a direction transverse of the longitudinaldirection of said belt, the third member of said loop coils positionedlongitudinally adjacent to said first and second members and including apair of coil sides extending in the longitudinal direction of said beltin spaced parallel relation to each other, and a pair of coil sidesextending in a direction transverse of the longitudinal direction ofsaid belt in spaced parallel and adjacent relation to each other andwith one transverse coil sides of each of said first and second members,a pair of excitor coils connected to an oscillating current source andrespectively positioned in proximity to said parallel, adjacenttransverse sides of said first member, said second memberand said thirdmember, a receiver coil positioned in proximity with each of the othertransverse sidesof said first, second and third members, and connectedto a belt fissure detector circuit, whereby the occurrence of a fissurein said conveyor belt can be detected by said detector circuit.

11. A belt fissure detection apparatus comprising a plurality of pairsof first and second loop coils embedded in a conveyor belt and disposedat suitable intervals over the entire length of said belt, said firstloop coil of each of said pairs extended in the longitudinal directionof said conveyor belt and adjacent to and along one edge of saidconveyor belt and said second loop coil of each of said pairs extendedin a direction at right angles relative to said first loop coil, one endof said second loop coil being adjacently spaced from a correspondingend of said first loop coil, a carriage having wheel means rotatable ona pair of rails positioned in a direction normal to the longitudinaldirection of said belt, a pair of vertical support shafts for each ofsaid carriages, a guide roller rotatably mounted on the end of each ofsaid support shafts to engage a respective edge of said conveyor belt,tie rod means to couple said carriages together, said carriages havingmounted thereon an excitor coil and a pair of receiver coils in alignedrelationship to said loop coils, said receiving coils capable ofreceiving respective signals from said excitor coil through the loopcoils, and a fissure detector signal connected to said receiver coilsand responsive to said signals therefrom indicative of the occurrence offissure in said conveyor belt.

12. A belt fissure detection apparatus comprising a v a plurality ofpairs of first and second elongated loop coils embedded in a conveyorbelt at various intervals over the entire length of said conveyor beltsaid first loop coil of each pair extended in the longitudinal directionof said conveyor belt and adjacent to and along one edge of saidconveyor belt,

said second coil of each pair extended in a direction transverse to thelongitudinal length of said conveyor for substantially the entire widththereof one coil end of said second loop coils in close proximity to oneend of said first loop coils.

13. The belt fissure detection apparatus of claim 12 characterized inthat said one coil end of said first and second loop are in overlayedrelation within said conveyor belt.

14. The belt fissure detection apparatus-of claim 12 characterized inthat said loop coils are of quadrangular configuration.

15. The belt fissure detection apparatus of claim 12 characterized by afissure detector circuit comprising an excitor coil connected to acurrent source and a pair of receiver coils connected to a fissuredetection circuit means, said excitor coil positioned relative to saidconveyor belt to be in electromagnetic coupling to said one end of eachof said pair of first and second loop coils as said conveyor belt isdriven, each of said receiver coils positioned relative to said conveyorbelt to be in electromagnetic coupling to the respective other ends ofeach of said pairs of first and second loop coils as said conveyor beltis driven, said circuit detection means responsive to signals receivedfrom said receiver coils from said excitor through said first and secondloop coils indicative of the nonoccurrence of a fissure in said conveyorbelt.

16. The belt fissure detection apparatus of claim 15 characterized byconveyor belt tracking means to support said excitor and receiver coilsto compensate for lateral meandering of said conveyor belt while thelatter is being driven to maintain said coils at all times inelectromagnetic coupling relation with said loop coil ends.

17. The belt fissure detection apparatus of claim 15 characterized inthat said fissure detection circuit means includes circuit gate means toreceive receiver signals,

a bistable flip-flop network set and reset by the respective outputsignals of said circuit gate means; said flip-flop network productive ofan output signal when one of said receiver signals is not received atsaid circuit gate means, and comparator circuit means connected toreceive said flipfiop network output signal and operative of anannunciator when said output signal is greater than a predeterminedvalue.

1. A belt fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire length of said belt, said first loopcoil extended in the longitudinal direction of said conveyor belt andadjacent to and along one edge of said conveyor belt and said secondloop coil extended in a direction at right angles relative to said firstloop coil, one end of said second loop coil being overlapped by acorresponding end of said first loop coil adjacent to said conveyor beltedge, and excitor coil connected to an oscillating current source andpositioned in proximity to said overlapped loop coil ends of said firstand second loop coils, a pair of receiver coils connected to respectiveterminals of a belt fissure detector circuit and positioned in proximityto the other ends of said first and second loop coils, the arrangementof all of said coils being such that, when said overlapped loop coilends travel in proximity near said excitor coil as said conveyor belt isbeing driven, said other loop coil ends at the same time travel inproximity with respective of said receiver coils to provide anelectromagnetic coupling circuit between said excitor coil and saidreceiver coils through said loop coils to produce a pair of electricalsignals whereby the occurrence of a fissure in said conveyor belt can bedetected by said detector circuit.
 2. The belt fissure detectionapparatus of claim 1 wherein said electric signals received by saidreceiver coils are respectively applied to an ''''OR'''' circuit and an''''AND'''' circuit, in said detector circuit the output signal of saidOR circuit being applied to a set terminal of a bistable flip-flopcircuit while the output signal of said AND circuit applied to a resetterminal of said bistable flip-flop circuit through a delay circuit, theoutput signal of said flip-flop circuit being representative of abreakage of any one of said loop coils embedded in said conveyor belt.3. The belt fissure detection apparatus of claim 1, wherein each of saidloop coils embedded in said conveyor belt comprises a wiring elementconsisting of a resilient fiber core and a fine conductive wire in theform of strip or foil spirally wound around said core.
 4. The beltfissure detection apparatus of claim 1, wherein each of said loop coilsembedded in said conveyor belt comprises a wiring element consisting oftwo lengths of twisted fine conductive wire in the form of strip or foilspirally wound around a resilient fiber core.
 5. The belt fissuredetection apparatus of claim 1, wherein each of the loop coils comprisesa wiring element consisting of a resilient fiber core and a plurality offine conductive wires in the form of a foil spirally wound around saidcore, said plurality of wires being arranged in parallel alignment andbound together by shoot yarns to provide a band.
 6. The belt fissuredetection apparatus of claim 1, wherein each of said receiver coils orsaid excitor coil comprises a primary winding formed around a ferritecore and a secondary winding formed around said ferrite core adjacentsaid primary winding, said secondary coil winding forming a resonancecircuit in resonance with the excitor frequency imposed upon saidprimary coil.
 7. A belt fissure detection apparatus comprising aplurality of pairs of first and second loop coils embedded in a conveyorbelt and disposed at suitable intervals over the entire length of saidbelt, said first loop coil extended in the longitudinal direction ofsaid conveyor belt and adjacent to and along one edge of said conveyorbelt and said second loop coil extended in a direction at right anglesrelative to said first loop coil, one end of said second loop coil beingadjacently spaced from a corresponding end of said first loop coil anexcitor coil connected to an oscillating current source and positionedin proximity to both of said spaced loop coil ends of said first andsecond loop coils, a pair of receiver coils connected to respectiveterminals of a belt fissure detector circuit and positioned in proximityto the other ends of said first and second loop coils, the arrangementof all of said coils being such that, when said spaced loop coil endstravel in proximity near said excitor coil as said conveyor belt isbeing driven, said other loop coil ends at the same time travel inproximity with respective of said receiver coils to provide anelectromagnetic coupling circuit between said excitor coil and saidreceiver coils through said loop coils, whereby the occurrence of afissure in said conveyor belt can be detected by said detector circuit.8. A belt fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire length of said belt, said first loopcoil first extended in the longitudinal direction of said conveyor beltand adjacent to and along one edge of said conveyor belt and said secondloop coil extended in a direction at right angles relative to said firstloop coil, one end of said second loop coil being adjacently spaced froma corresponding end of said first loop coil, an excitor coil capable ofgenerating two electrical signals of different frequencies andpositioned in proximity to said adjacently spaced first and second loopcoil ends, a pair of receiver coils connected to respective terminals ofa fissure detector circuit and positioned in proximity to the other endsof said first and second loop coils, the arrangement of all said coilsbeing such that, when said adjacently spaced loop coil ends travel inproximity to said excitor coil as said conveyor belt is driven, saidother loop coil ends at the same time travel in proximity withrespectiVe of said receiver coils to provide an electromagnetic couplingcircuit between said excitor coil and said receiver coils through saidloop coils, whereby signals received by said receiver coils are appliedto circuit filter means for discriminating between said signals due todifferent frequencies and thereafter applied to respective terminals ofsaid detector circuit.
 9. A belt fissure detection apparatus comprisinga pair of loop coils embedded in a conveyor belt, one of said coilsextended in the longitudinal direction of said belt and adjacent to andalong one edge of said belt, the other of said coils extended in adirection transverse to the longitudinal direction of said belt andhaving one end in overlapped relationship with one end of thefirst-mentioned loop coil, a second pair of loop coils embedded in saidbelt at a position adjacent to the first-mentioned pair of loop coils,one of said coils of said second loop coil pair extended in thelongitudinal direction of said belt, the other of said coils of saidsecond loop coil pair extended in a direction transverse to thelongitudinal direction of said belt and having one end in overlappedrelationship with one end of the first-mentioned loop coil of saidsecond loop coil pair, excitor coils each capable of generating anelectric signal of oscillating current and each respectively positionedin proximity to one of said overlapped ends of said first and secondloop coil pairs, two pairs of receiver coils, each pair connected torespective terminals of a fissure detector circuit and each respectivelypositioned in proximity to the other ends of said loop coils of each ofsaid loop coil pairs, the arrangement of all of said coils being suchthat, when said overlapped loop coil ends of each of said loop coilpairs travel in proximity near their respective excitor coil as saidconveyor belt is driven, said other ends of said loop coils of each ofsaid loop coil pairs at the same time travel in proximity to theirrespective receiver coils to provide an electromagnetic coupling circuitbetween each of said excitor coils and each of said receiver coilswhereby the occurrence of a fissure in said conveyor belt can bedetected by said detector circuit.
 10. A belt fissure detectionapparatus comprising a plurality of loop coil members each ofquadrangular configuration and together comprising one unit embedded ina conveyor belt and disposed at suitable intervals over the entirelength of said belt, the first member of said loop coils including apair of coil sides extending in the longitudinal direction of said beltin spaced parallel relation to each other and a second pair of the coilsides extending in a direction transverse of the longitudinal directionof said belt, the second member of said loop coils including a pair ofcoil sides extending in the longitudinal direction of said belt inspaced parallel relation to each other, one of said coil sides in spacedparallel and adjacent relation to one of the longitudinal coil sides ofsaid first member, and a second pair of coil sides extending in adirection transverse of the longitudinal direction of said belt, thethird member of said loop coils positioned longitudinally adjacent tosaid first and second members and including a pair of coil sidesextending in the longitudinal direction of said belt in spaced parallelrelation to each other, and a pair of coil sides extending in adirection transverse of the longitudinal direction of said belt inspaced parallel and adjacent relation to each other and with onetransverse coil sides of each of said first and second members, a pairof excitor coils connected to an oscillating current source andrespectively positioned in proximity to said parallel, adjacenttransverse sides of said first member, said second member and said thirdmember, a receiver coil positioned in proximity with each of the othertransverse sides of said first, second and third members, and connectedto a belt fissure detector circuit, wherebY the occurrence of a fissurein said conveyor belt can be detected by said detector circuit.
 11. Abelt fissure detection apparatus comprising a plurality of pairs offirst and second loop coils embedded in a conveyor belt and disposed atsuitable intervals over the entire length of said belt, said first loopcoil of each of said pairs extended in the longitudinal direction ofsaid conveyor belt and adjacent to and along one edge of said conveyorbelt and said second loop coil of each of said pairs extended in adirection at right angles relative to said first loop coil, one end ofsaid second loop coil being adjacently spaced from a corresponding endof said first loop coil, a carriage having wheel means rotatable on apair of rails positioned in a direction normal to the longitudinaldirection of said belt, a pair of vertical support shafts for each ofsaid carriages, a guide roller rotatably mounted on the end of each ofsaid support shafts to engage a respective edge of said conveyor belt,tie rod means to couple said carriages together, said carriages havingmounted thereon an excitor coil and a pair of receiver coils in alignedrelationship to said loop coils, said receiving coils capable ofreceiving respective signals from said excitor coil through the loopcoils, and a fissure detector signal connected to said receiver coilsand responsive to said signals therefrom indicative of the occurrence offissure in said conveyor belt.
 12. A belt fissure detection apparatuscomprising a plurality of pairs of first and second elongated loop coilsembedded in a conveyor belt at various intervals over the entire lengthof said conveyor belt said first loop coil of each pair extended in thelongitudinal direction of said conveyor belt and adjacent to and alongone edge of said conveyor belt, said second coil of each pair extendedin a direction transverse to the longitudinal length of said conveyorfor substantially the entire width thereof one coil end of said secondloop coils in close proximity to one end of said first loop coils. 13.The belt fissure detection apparatus of claim 12 characterized in thatsaid one coil end of said first and second loop are in overlayedrelation within said conveyor belt.
 14. The belt fissure detectionapparatus of claim 12 characterized in that said loop coils are ofquadrangular configuration.
 15. The belt fissure detection apparatus ofclaim 12 characterized by a fissure detector circuit comprising anexcitor coil connected to a current source and a pair of receiver coilsconnected to a fissure detection circuit means, said excitor coilpositioned relative to said conveyor belt to be in electromagneticcoupling to said one end of each of said pair of first and second loopcoils as said conveyor belt is driven, each of said receiver coilspositioned relative to said conveyor belt to be in electromagneticcoupling to the respective other ends of each of said pairs of first andsecond loop coils as said conveyor belt is driven, said circuitdetection means responsive to signals received from said receiver coilsfrom said excitor through said first and second loop coils indicative ofthe nonoccurrence of a fissure in said conveyor belt.
 16. The beltfissure detection apparatus of claim 15 characterized by conveyor belttracking means to support said excitor and receiver coils to compensatefor lateral meandering of said conveyor belt while the latter is beingdriven to maintain said coils at all times in electromagnetic couplingrelation with said loop coil ends.
 17. The belt fissure detectionapparatus of claim 15 characterized in that said fissure detectioncircuit means includes circuit gate means to receive receiver signals, abistable flip-flop network set and reset by the respective outputsignals of said circuit gate means; said flip-flop network productive ofan output signal when one of said receiver signals is not received atsaid circuit gate means, and comparator circuit Means connected toreceive said flip-flop network output signal and operative of anannunciator when said output signal is greater than a predeterminedvalue.